Process for the preparation of molybdenum-containing oxidation catalysts

ABSTRACT

Molybdenum containing oxidation catalysts are prepared by reducing hexavalent molybdenum to a valence state below +6 prior to or during the catalyst preparation. Reproducible catalysts with superior catalytic activity are conveniently made by this process.

Frech et al.... 252/467 I, Umted States Patent 1191 1111 3,928,240

Milberger et a1. Dec. 23, 1975 1 PROCESS FOR THE PREPARATION OF3,117,097 1/1964 .Ianoski 252/467 MQLYBDENUM CO OXIDATION 3,169,919 2/1965 Gatsis et a1. 252/467 3,336,100 8/1967 Cloppet 423/606 CATALYSTS3,351,423 I 11/1967 Zimmerley et a1 423/606 [75] Inventors: Ernest C.Milberger, Solon; Serge R. 3,542,842 11/ 1970 Grasselli et a1. 252/467Dolhyj, a both of Ohio 3,551,470 12/1970 Shaw et a1. 252/467 3,574,7294/1971 Gasson 252/467 Asslgneei The Standard 0 p y 3,595,911 7/1971 Ball252/467 Cleveland, 01110 3,631,104 12/1971 Habermann et a1. 252/4673,644,509 2/1972 Allen 252/467 [22] i 1973 3,676,332 7/1972 Johnson252/467 [211 PP Q 391,775 FOREIGN PATENTS ORAPPLICATIONS Related U.S.-Application Data 4,523,615 1970 Japan 3 continuatiomimpafl of sen177,105, Sept 1 381,570 10/1932 Umted Kingdom 252/467 1 1971- I v 1 7OTHER PUBLICATIONS 52 us. c1. 252/467; 260/346.8; 260/530 N; P P86405730 7/5/69' N 7 1 423/606 252/465 2'52/468 252,470 Ishn et a1.,Chemical Abstracts, 69(1968), o. 0 83. [51] Int Cl 2 1 B0 5 23/l8 Suzuk1et a1., Chemical Abstracts, 74(1971), No.

, B01] 23 24 1 1 v[58] Field of Search 252/4 7i 423 0 2 ChemicalAbstracts, p. 196833, 8th collective index.

5 1 References Cited Primary Examiner-Arthur P. Demers UNITED STATESPATENTS Attorney, Agent, or Flrm-Herbert D. Knudsen 2,124,388 7/1938Weiss et a1 252/467 I 2,572,300 10/195l Arnold et a1 252/467 2,692,29310/1954 I-Ieinemann.....'. 252/467- [57] ABSTRACT, 2,749,366 6/1956,Foster et a1 252/467 Molybdenum containing oxidation catalysts are pre-2,765,263 10/1956 Fritz et'al. 252/467 pared by reducing hexavalentmolybdenum to a va- 2,814,650 11/1957 Clark 252/467 len e tate below +6prior to or during thecatalyst et a1. preparatior Reproducible catalystssuperior at 3:12:15 alytic activity are conveniently made by thisprocess. 9 Claims, No Drawings PROCESS FOR THE PREPARATION OFMOLYBDENUM-CONTAINING OXIDATION CATALYSTS CROSS REFERENCE TO RELATEDAPPLICATION This application is a continuation-in-part of our priorapplication Ser. No. 177,105 filed Sept. 1, 1971, with Harley F.l-Iardman. Our pn'or application is hereby incorporated by reference.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION It has now beendiscovered in the process for the preparation of oxidation catalystscontaining molybdenum using a compound containing hexavalent molybdenum,the, improvement comprising partially reducing the molybdenum in thecompound containing hexavalent molybdenum to avalence state below +6with a reducing agent before or during the preparation of the catalyst.Usingthe present invention, catalysts of enhanced activity andselectivity and more reproducible preparations result.

The central aspect of the present invention is the reduction of themolybdenum in the compound containing hexavalent molybdenum employed inthe preparation of oxidation catalysts. This lower oxidation state isstabilized and retained during subsequent catalyst preparation steps,such as calcination at temperatures above 200C. It is the discovery ofthe invention that catalysts containing reduced molybdenum are superiorto and easier to prepare than the catalysts of the art.

Once the thrust of the invention is known, those of ordinary skill inthe ai't are capable of determining a number of procedures, reducingagents and degrees of reduction that would be suitable for use in thepresent invention. Therefore, it is not necessary to describe allpossible means for accomplishing the reduction, for one of ordinaryskill could accomplish the reductions with little or no experimentation.

Broadly, any conditions or reducing agent may be used so long as thebasic nature of the catalyst is not adversely affected. Even thoughthere is a large number of alternative procedures by which thesecatalysts can be made, procedures that have been found to be preferredwill be discussed in detail below. y

A preferred method of reduction involves the contact of the compoundcontaining hexavalent molybdenum with a controlled amount of a strongreducing agent. For example, molybdenum trioxide could be contacted inan aqueous suspension with a given amount of tungsten metal powder toeffect a certain and reproducible degree of reduction.

5 an aqueous suspension of antimony trioxide and molybdenum trioxidecould be refluxed for a number of hours. The amount of water in such apreparation is not critical, but about 500 to about 2000 milliliters permole of molybdenum trioxide reacted has been found to give good results.

During the reductions of the present invention, it has been observedthat the water containing the hexavalent molybdenum changes color. It isbelieved that this change in color is an indication that the molybdenumis being reduced.

There is substantially no limit on the reducing agents that could beemployed to reduce the compound containing hexavalent molybdenum. A widerange of reducing agents are known that could reduce hexavalentmolybdenum. Representative examples of strong reducing agents includefinely divided or colloidal metals such as molybdenum, tungsten,magnesium, aluminum or nickel stannous ion; sulfur dioxide, organicreducing agents, hydrazine hydrate and the like. Representative examplesof weak reducing agents are lower valent antimony oxides and salts andother metal oxides or salts containing metals in their lower oxidationstates.

The amount by which the hexavalent molybdenum is reduced may vary asdifferent catalysts are employed. The important feature of the inventionis that the hexavalent molybdenum is reduced until a significantlyimproved catalyst or preparation is obtained. In a preferred practiceofthe invention, enough reducing agent is employed so that the valencerequirements of the hexavalent molybdenum is reduced by about 0.2 toabout 20%. When powdered metals, such as tungsten or molybdenum, areemployed, the amount of metal preferably reactedis about 0.01 to about10 atom percent per mole of hexavalent molybdenum present.

The catalytic components other than molybdenum are convenientlyincorporated into the catalyst after the reduction step of the presentinvention. Alterna-. tively, the other catalytic components are presentduring the reduction of the hexavalent molybdenum. The presence of otherelements during the reduction is acceptable so long as these otherelements do not interfere with or are not adversely affected by thereduction. After the reduction step of the present invention and theincorporation of other required elements, the catalysts are normallycalcined at a temperature between about 350 and about 650C. into thefinal form of the catalyst. The reduced molybdenum is not adverselyaffected by these subsequent treatments.

The other aspects of the invention are not critical. The central aspectof the invention is the reduction of hexavalent molybdenum as discussedabove. The following discussion, however, describes some of the othervariables.

As noted, the present invention prepares oxidation catalysts containingmolybdenum. The structure of the catalyst may range from a simplemolybdenum oxide catalyst to a complex multicomponent catalyst. Anycatalyst containing molybdenum could be prepared by the process of theinvention. The preferred catalysts of the present invention are thoseused in the oxidation, ammoxidation and oxidative dehydrogenation ofolefins, diolefins, aldehydes and aromatic compounds. Representativeexamples of such reactants are propylene, butylenes, butadiene,iosamylene, acrolein, methacrolein, benzene and methyl substitutedbenzenes. Using the catalyst preparation of the present invention, thesecatalysts are improved, the catalysts are conveniently reproduced andthe lower oxidation state of the molybdenum is stabilized and retainedduring calcination procedures.

SPECIFIC EMBODIMENTS Comparative Example A and Examples 1-11 Effect ofreduced catalyst on the preparation of maleic anhydride The effect ofusing a catalyst containing reduced molybdenum was examined for acatalyst of Sb Mo O in the oxidation of butadiene to obtain maleicanhydride. The catalysts were prepared as follows:

Comparative Example A 288 grams of M and 194.3 grams of Sb O were ballmilled for 24 hours. The mix was screened through a 200 mesh sieve andthen pelleted. The pellets were calcined in air for one hour at 65C. andthen for 2% hours at 400C.

Examples 1 and 2 Four separate batches each containing 143.9 gramsmolybdenum trioxide and 97.2 grams antimony trioxide were refluxed in1000 mls. distilled water for 2 /2 hours and were evaporated and driedovernight at 120C. The dried materials were mixed together, then groundand screened to 20/30 mesh. The resulting material was hard and olivegreen in color. The catalyst was calcined at aobut 425C. for 2 hours.

Example 3 72 grams of M00,- and 0.95 grams of molybdenum metal powder(99.8%) were slurried in 1000 mls. of distilled water and refluxed for 2hours. 48.6 grams of Sb O were then added, and refluxing continued foran additional 2 hours. The slurry was then evaporated to a thick paste,which was then dried overnight at 110C. The resulting darkgreenish-black material was ground and screened to 20-30 mesh. Thecatalyst was pretreated as in Example 1.

Example 4 72 grams of M00 0.95 grams of molybdenum metal powder and 48.6grams of Sb O were slurried in 1 liter of distilled water. The slurrywas refluxed for 3 hours and then evaporated to a thick paste. Thecatalyst was then dried overnight at 110C. and ground and screened to20-30 mesh. The catalyst was pre-treated as in Example 1.

Example 5 72 grams of M00 and 48.6 grams Sb O were slurried in one literof distilled water. The slurry was refluxed for three hours. To thisslurry was added 0.95 grams of molybdenum metal powder and refluxing wascontinued for one hours. The slurry was then evaporated. dried andscreened to -30 mesh. The catalyst was pre-treated as in Example 1..

Example 6 0.12 4 6 2-a.4 The procedure of Example 3 was repeated.

Example 7 Example 8 The procedure of Example 3 was used except that 0.24gram of magnesium metal powder was employed in place of the molybdenumpowder.

Example 9 The procedure of Example 3 was employed except that 0.27 gramof aluminum metal powder was used in place of molybdenum powder.

Example 10 The procedure of Example 3 was employed except that 0.59grams of nickel metal powder was used in place of the molybdenum powder.

Example 1 1 The preparation was the same as in Example 3 except that0.75 gram of hydrazine hydrate was used in place of the molybdenumpowder.

These catalysts were tested for effectiveness in the oxidation ofbutadiene to maleic anhydride in a 20 cc. fixed-bed, down-flow reactorconstructed of a length of one-half inch stainless steel tubing. Thereactor was heated with a split stainless steel block furnace.

The primary receiver consisted of a 500 milliliter flask whichfunctioned as an air condenser and most of the maleic anhydride wascollected therein as a solid. The non-condensible gases passed through awater scrubber, and the unabsorbed gases were vented.

Product analyses of the aqueous scrubber liquid were conducted bydetermining total acid content by titration with standard base (0.1Nsodium hydroxide) and maleic anhydride was determined by gravimetricprecipitation of barium maleate. The scrubber liquid which containedcarbonyl products such as acetaldehyde, furan, acrolein, methyl ethylketone, crotonaldehyde and acetone was analyzed by gas chromatographyusing a three-foot Poropak QS column in a F & M 810 ResearchChromatograph. The analyses of the liquid products were conducted bycomparing the response of the unknown sample with that of a standard.

The gravimetric method for analyzing maleic anhydride consisted ofmixing 25 milliliters of the scrubber solution with 20 milliliters of asolution of 5% BaCl-2- H 0 and adding concentrated ammonium hydroxide toobtain a phenolphthalein color reaction. The solution was then dilutedto milliliters with absolute alco hol. The filtered precipitate wasdried at 1 10C. for 2 to 3 hours, and the maleic anhydride wascalculated as barium maleate monohydrate according to the methoddescribed in J. Am. Chem. Soc. 57, 1390, 1935.

The results of these experiments are given in Table l. The percent perpass conversion to maleic anhydride is 5 defined as follows:

on a single pass of the starting material over the catalyst,

Grams of carbon as maleic anhydride obtained Grams of carbon as organicstarting material fed x 100 Table I i Examples 12 and 13 IMPROVEMENTRESULTING FROM USIN(.i-Sb Mo,;O- CATALYSTS CONTAINING REDUCEDMOLYBDENUM" IN THE PREPARATION OF MALEIC ANHYDRIDE FROM BUTADIENE MoleBath Per Pass Conversions to Reducing Temp Air/BD C.T.; Total MaleicExample Agent C moles sec. WWH Acid An hydride Comp. A none 385 30 2.247.0 1 Sb,0 371 v 27: 312 0.024 58.0 54.5 2 399 26 3.0 0.025 58.9 57.3 3M6,, 371 33 3.1 0.066 77.3 76.6 4 371 33 3.1 0.021 70.1 70.9 5 371 303.1 0.023 69.9 64.5 6 371 33 3.2 0.060 77.6 74.3 7 w, 371 26 3.1 0.06174.4 68 .9 8 M1;M 399 27 3.0 0.050 68.0 61.9 9 A1 399 27 3.0 0.051 71.365.3 10 Ni 399 30 3.0 0.042 63.9 l 1 hydrazine 371 22 3.2 0.068 73.5

hydrate 3 i Comparative Examples B-D and Examples 12-15 ComparativeExamples B and C.

Unreduced Mo 72 grams of M00 13.37 grams of V 0 and 12.50 grams of H WOwere'slurried in 750 cc. of distilled water and refluxed for 2 hours. Nocolor change was observed. 146.8 grams of Nalco silica sol (40% SiO wasadded. The slurry was evaporated to a thick paste, which was then driedovernight at l C. The resulting dark yellow material was ground andscreened to /30 mesh and pre-treated in a reactor under airflow for 2hours at 399C.

silica sol (34% SiO was added. The slurry was evaporated to a thickblue-black paste, which was dried overnight at C. The resultingdark-green material was pretreated as in Examples B and C.

Comparative Example D Unreduced Mo 88.6 grams of (Nl-I Mo-,O .4H O,13.48 grams (NI-I )W-,O .6I-I O, 14.62 grams NI-LVO and 145.5 grams of,Nalco silica sol (40% SiO were dissolved in 735 cc. distilled water andevaporated to a thick orange paste, then dried ovemight at -110C. Theresulting material was ground and screened to 20/30 mesh. The catalystwas pre-treated in a reactor under air flow by heating slowly within 3hours from room temperature to 399C., then keeping for approximately 4additional hours at 399C. j

Examples 14 and 15 Reduced M0 The catalyst was prepared in an identicalmanner as Comparative Example D, except 9.19 gramstungsten metal powderwas ,used as the W source. The color of the solution changed to darkblue-black. The dried material was pro-treated in a reactor as inExample D.

Using the reactor of the examples above, the oxidation of acrolein toacrylic acid was conducted. The conditions and results of such reactionsare shown in Table II.

Table II EFFECT OF REDUCED MOLYBDENUM CATALYSTS ON THE OXIDATION OFACROLEIN TO ACRYLIC ACID Feed/Mole Molar Per Pass Temp., C. of AcroleinC.T., Unreacted Conversion to Example Bath Exotherm Air H O Sec.Acrolein Acrylic Acid Comp. B 260 265 10.3 6.2 2.0 69.0 24.9 Comp. C 343354 1.7 7.0 50.3 12 260 283 10.2 6.1 2.0 truce 80.3 13 246 256 2.1 4.286.3 Comp. D 274 289 10 6 l 9 0.4 80.4 14 260 281 10.3 6.2 2 0 0.3 86.2

Table II-continued EFFECT OF REDUCED MOLYBDENUM CATALYSTS ON THEOXIDATION OF ACROLEIN TO ACRYLIC ACID Comparative Examples E and F andExamples 15 and 16 Comparison in the Preparation of Methacrylic Acid Theconditions and results of these experiments in the fixed-bed reactor ofthe examples above are given in Table III. The feed ratio ofmethacrolein/air/steam was 1/8/8 for all examples.

Table Ill EFFECT OF REDUCED MOLYBDENUM CATALYSTS ON THE OXIDATION OFMETHACROLEIN TO METHACRYLIC ACID Per Pass Conversion Temp., C. C.T.Unreacted to Methacrylic Example Bath Exotherm Sec. Methacrolein AcidComp. E 371 377 4.5 61.5 17.6 Comp. F 399 402 4.3 54.1 18.4 15 371 3714.5 63.2 22.2 16 399 402 d 4.3 44.0 21.5

from Me'thacrolein A demonstration of the superiority of the reduced Weclaim:

catalysts of the invention for the conversion of methacrolein tomethacrylic acid using a catalyst of Sb Mo P 0,. was made. The catalystwere prepared as follows:

Comparative Examples E and F Unreduced Mo 1 72 grams of M00 was slurriedin 500 ml. distilled water. 4.8 grams of 85% phosphoric acid was added,and the mixture was refluxed overnight. Color turned yellow with only asmall amount of undissolved residue remaining. 48.6 grams of Sb O wasadded with a resulting color change to green then to dark blue. This wasrefluxed for several hours, and then evaporated to a dark blue paste.The paste was dried overnight at 1 C. the dark blue material was groundand screened to 20/30 mesh. Prior to use, the catalyst was pretreated inthe reactor with an air flow for 2 hours at 427C.

Examples and 16 Reduced Mo 72 grams of M00; was slurried in 1000 ml.distilled water and 4.8 grams of 85% phosphoric acid was added. Themixture was heated to boiling. Color changed to yellow. 0.96 grams offinely powdered molybdenum metal powder was added and color changedimmediately to dark blue. Boiling was continued until the volume hadbeen reduced to 500 ml. 48.6 grams of Sb O and the slurry was refluxedfor two hours with no additional color change. The mixture was thenevaporated to a thick homogenous paste and subsequently dried overnightat l 10C. The deep dark blue cake was ground and screened to 20/30 mesh.The catalyst was pre-treated in the same manner as above.

LII

1. In the process for the preparation of oxidation catalysts containingantimony, molybdenum and oxygen or vanadium, molybdenum and oxygen ortungsten, molybdenum and oxygen, using an aqueous solution or slurry ofa compound containing hexavalent molybdenum, the Improvement comprisingpartially reducing in the aqueous solution or slurry the molybdenum inthe compound containing hexavalent molybdenum to a valence state below+6 with a reducing agent capable of reducing hexavalent molybdenum.

2. The process of claim 1 wherein the catalyst contains antimony,molybdenum and oxygen.

3. The process of claim 1 wherein the catalyst contains vanadium,tungsten. molybdenum and oxygen.

4. The process of claim 1 wherein the compound containing hexavalentmolybdenum is molybdenum trioxide or ammonium heptamolybdate.

5. The process of claim 1 wherein the compound containing hexavalentmolybdenum is molybdenum trioxide.

6. The process in claim 1 wherein the reducing agent is a memberselected from the group consisting of finely divided metal, an organicreducing agent, hydrazine hydrate, stannous ion and sulfur dioxide.

7. The process in claim 6 wherein the finely divided metal ismolybdenum.

8. The process in claim 6 wherein the finely divided metalis tungsten.

9. The process of claim 1 wherein the catalyst is prepared by refluxingan aqueous mixture of the compound containing hexavalent molybdenum anda reducing agent.

1. IN THE PROCESS FOR THE REPARATION OF OXIDATION CATALYSTS CONTAININGANTIMONY, MOLYBDENUM AND OXYGEN OR VANADIUM. MOLYBDENUM AND OXYGEN ORTUNGSTEN, MOLYBDENUM AND OXYGEN, USING AN AQUEOUS SOLUTION OR SLURRY OFA COMPOUND CONTAINING HEXAVALENT MOLYBDENUM, THE IMPROVEMENT COMPRISINGPARTIALLY REDUCING IN THE AQUEOUS SOLUTION OR SLURRY THE MOLYBDENUM INTHE COMPOUND CONTAINING HEXAVALENT MOLYBDENUM TO A VALENCE STATE BELOW+6 WITH A REDUCING AGENT CAPABLE OF REDUCING HEXAVALENT MOLYBDENUM. 2.The process of claim 1 wherein the catalyst contains antimony,molybdenum and oxygen.
 3. The process of claim 1 whrein the catalystcontains vanadium, tungsten, molybdenum and oxygen.
 4. The process ofclaim 1 wherein the compound containing hexavalent molybdenum ismolybdenum trioxide or ammonium heptamolybdate.
 5. The process of claim1 wherein the compOund containing hexavalent molybdenum is molybdenumtrioxide.
 6. The process in claim 1 wherein the reducing agent is amember selected from the group consisting of finely divided metal, anorganic reducing agent, hydrazine hydrate, stannous ion and sulfurdioxide.
 7. The process in claim 6 wherein the finely divided metal ismolybdenum.
 8. The process in claim 6 wherein the finely divided metalis tungsten.
 9. The process of claim 1 wherein the catalyst is preparedby refluxing an aqueous mixture of the compound containing hexavalentmolybdenum and a reducing agent.